Place egg whites in a large bowl; let stand at room temperature for 30 minutes. Meanwhile, line a greased 15-in. x 10-in. x 1-in. baking pan with waxed paper; grease the paper and set aside. Add vanilla, cream of tartar and salt to egg whites; beat on medium speed until soft peaks form. Gradually beat in sugar, 2 tablespoons at a time, on high until stiff glossy peaks form and sugar is dissolved. Fold in flour, about 1/4 cup at a time. Carefully spread into prepared pan. Bake at 350° for 15-20 minutes or until cake springs back when lightly touched. Cool for 5 minutes. Turn cake onto a kitchen towel dusted with confectioners’ sugar. Gently peel off waxed paper. Roll up cake in the towel jelly-roll style, starting with a long side. Cool completely on a wire rack. For filling, in a large saucepan, combine the cranberries, sugar and 1/4 cup water. Bring to a boil. Reduce heat; simmer, uncovered, for 5-6 minutes or until berries pop. Mash berries; strain, reserving juice and discarding pulp. Return juice to the pan. Combine cornstarch and remaining water until smooth; gradually add to cranberry juice. Bring to a boil; cook and stir for 2 minutes or until thickened. Chill. Unroll cake and spread filling to within 1/2 in. of edges. Roll up again. Cover and refrigerate for 1 hour before serving. Refrigerate leftovers. Yield: 12 servings.